I too have the same problem. According to the Metahuman documentation:
A LOD uses a particular geometric representation of the hair, from strands for high quality, to cards, to meshes (also called a helmet). Each LOD is represented in the following ways:
LOD 0–1 use strand-based geometry on high-end platforms (Xbox Series X, PlayStation 5, and PC), but also supports card representations for other platforms.
LOD 2–4 use card-based representations.
LOD 5–7 use simplified hair meshes.
The fact that the hair disappears as soon as the camera goes too far way, suggests that LOD 2+ isn’t set up. Maybe the Metahuman creator has not exported hair cards and simplified meshes. I have not checked to see if this is the case.